Neutrophils provide the body's first line of defense against infection. They fight infections by, among other things, releasing chemokines or cytokines which initiate cascades of other immune mediators and cell types. Neutrophils themselves are first signaled to move to the site of infection via chemokines. Once they arrive at the infection site, the neutrophils are activated. This activation can take many forms: increased exocytosis and phagocytosis, extension of their life span, and alteration of adhesion molecules for enhancing their specificity and mobility. Although the rapid response and flexibility of neutrophils make them an integral part of the body's immune system, human cytomegalovirus (HCMV), ironically, may use neutrophil activation for its own evolutionary advantage. HCMV may use neutrophils for dissemination or for attracting other cell types within which HCMV can remain latent. Virulent HCMV produces a functional chemokine, vCXCL-1Tol, that can mimic the body's normal immune response by attracting and activating neutrophils, yet this chemokine is only 22% identical to the host ELR-CXC chemokine, Gro&#945;. The gene for this viral chemokine is one of the most variable in the HCMV genome with the vCXCL-1 proteins from different isolates having as little as 32% identity with each other. Using viral chemokines from a transplant patient and AIDS patients, we will compare these viral chemokines to chemokines from virulent and attenuated CMV strains. The questions that we will address are: 1) Do these viral chemokines have unique binding and functional outcomes? 2) Do these differences relate to viral pathogenesis in vivo? We have expressed and isolated the vCXCL-1 proteins from four different clinical isolates representing divergence in the vCXCL-1 family. Our next step will be to assess the differences in viral chemokine receptor usage, binding and signaling characteristics, and cellular processes. Initially we will focus on the variant chemokine from the C956 strain, which has the least homology to vCXCL-1Tol and the chemokine from the avirulent Towne strain. We will then relate these in vitro differences to the role that these proteins play in viral dissemination and pathogenesis using murine CMV as a surrogate for the HCMV chemokine genes. By understanding how these novel viral chemokines function in vitro and in vivo, we will begin to understand more about the complex relationship between the CMV life cycle, its impact on neutrophil functions, and disease.